Powder coating compositions containing anhydride end-caped crystalline polyesters

ABSTRACT

Thermosetting coating compositions containing amorphous and semi-crystalline polyesters are provided. They are useful in coating compositions, especially for low temperature powder coating applications.

This invention relates to thermosetting coating compositions containinga carboxylic acid anhydride end-capped crystalline polyester in powdercoating applications, and more particularly in low temperature curepowder coating applications.

Powder coating applications are considered green chemistry processbecause their compositions greatly reduce or completely eliminate theorganic solvents used in liquid paints. When they are thermally cured,no or very little volatile organic compounds (VOC) are released to thesurrounding environment.

A typical thermoset powder coating formulation consists of a polymericbinder, curative, pigment, flow aid, degassing agent and curingcatalyst. Among all binders polyesters are widely used because theyprovide excellent weathering resistance and mechanical properties aswell as good appearance. Polyester resins have either hydroxyl orcarboxyl groups at their chain ends. Hydroxyl functional polyesters aretypically formulated with a blocked isocyanate curative to form apolyester-urethane powder coating. Carboxyl functional polyesters may beformulated with a crosslinker such as triglycidyl isocyanurate, TGIC,polyepoxy resins and other compounds or polymers which containfunctional groups reactable with carboxylic acid groups to formthermosetting networks. Powder coating compositions using carboxylatedpolyester and TGIC curative give coatings with good exterior durability,and the powder coatings using polyepoxy resins as curatives are mainlyfor interior applications. The polyester resins in powder coatingcompositions usually possess a glass transition temperature of above 50°C., which allows the powder coating composition to have storagestability without sintering.

Powder coating formulations are typically mixed, extruded, pulverized,classified and electrostatically applied onto substrates. The coatedparts are then baked at elevated temperatures.

Currently, the great majority of polyesters used in heat-curable powdercompositions are amorphous polyesters. When the polyester is amorphous,it is difficult to prepare perfect heat-curable powdered compositionsbecause they have to meet often contradictory criteria. Thus, thesepowders may not re-agglomerate during handling, transportation andstorage, which implies that the amorphous polyester must possess asufficiently high glass transition temperature (T_(g)). On the otherhand, in order for the powder particles to be able to coalesce and toform a perfectly homogeneous and uniform coating, it is necessary forthe T_(g) of the polyester to be sufficiently low to ensure a lowviscosity in the molten state which itself ensures good wetting of thepigments and other solid materials accompanying the polyester in theformulation of the said heat-curable powder compositions.

Moreover, the powder must be capable of melting at the stovingtemperature in order to form an even film before the crosslinkingreaction begins which results in the final curing. In order to obtaingood spreading of the molten film over the surface of the substrates, itis therefore necessary for the viscosity of the polyester in the moltenstate to be sufficiently low. This is because a very high viscosity inthe molten state prevents good spreading of the molten film and isreflected by a loss in the evenness and gloss of the coating. Finally,the rate of the crosslinking reaction is controlled by varying thetemperature, the amount and/or the nature of the curative and that ofthe curing catalyst, which is optionally used.

For all these reasons, it Is not generally recommended to producecoatings from compositions based on such amorphous polyesters by stovingat temperatures below 160° C. for approximately 10 to 20 minutes.

There is increasing market interest in applying powder coatings onheat-sensitive substrates such as wood, plastics and medium-densityfibreboard (MDF). In order to fulfil these needs, cure temperatures mustbe lowered to below 150° C. However, at low temperatures, powders tendto cure incompletely and do not flow effectively. Incomplete cure andpoor flow can cause many property defects such as adhesion failure, poorchemical resistance, poor mechanical properties, orange peel, etc.

Accordingly, it is an object of the present invention to providethermosetting powder coating compositions which, upon application andcuring at low temperatures, provide finishes which overcome all thesenegative aspects.

It now has been surprisingly found that a binder composition comprisinga carboxylic acid group containing amorphous polyester, a particularcarboxylic acid anhydride end-capped semi-crystalline polyester and aglycidyl group containing polyphenoxy resin curative, when applied andcured at temperatures of from 80 to 150° C. for 5-30 minutes, affordscoatings having good adhesion to metallic and non-metallic surfaces,excellent flow, outstanding flexibility and chemical resistance. Thecomposition can optionally contain one or more curing agents havingfunctional groups reactable with the polyesters' carboxylic acid groups,

Powder coating compositions based on semicrystalline polyesters havealready formed the subject of a certain number of publications in theform of papers and patents, in particular U.S. Pat. Nos. 4,352,924,3,387,214, 4,937,288 and 4,973,646.

EP 521992B1 describes a powder coating composition containing anamorphous and a semi-crystalline polyester resin. The semi-crystallineresin has an acid number of from 10 to 70 mg KOH/g. The purpose ofadding the crystalline polyester is to improve the flow of the powdercoating.

U.S. Pat. No. 4,937,288 describes a powder coating system having animproved flow property that consists of a carboxyl functional acrylicpolymer, a crystalline polyester and a beta-hydroxyalkylamide curingagent. The crystalline polyester has an acid number of from about 150 to750 mg KOH/g. The system is limited to beta-hydroxyalkylamide curativeand is not related to low-temperature cure powder coatings.

U.S. Pat. No. 6,407,181 describes a powder coating composition based ona glycidyl (meth)acrylate copolymer and a low-viscosity carboxylic acidfunctional polyester, which provides a smooth, weatherable, reducedgloss coating for use on heat sensitive substrates. According to thatpatent, the low-viscosity carboxylic acid functional polyesters aregenerally linear but may be capped with trimellitic anhydride to providea functionality of 4. The said polyesters have acid numbers between 20and 60 mg KOH/g, and glass transition temperatures between 40 and 800C.Depending upon the gloss reduction desired, the low viscosity polyesterscan be replaced by or blended with a crystalline polyester. Neither thecrystalline polyester nor the preparation of it was described in thepatent. The glycidyl (meth)acrylate containing copolymer is used as thehardener.

According to the current invention there are provided a thermosettingcoating composition comprising a binder wherein 100 parts by weight ofthis binder comprises:

(A) 1 to 50 parts by weight of a carboxylic acid group containingamorphous polyester having an acid number of from 15 to 100 mg KOH/g.

(B) 1 to 50 parts by weight of a carboxylic acid group containingsemi-crystalline polyester, said polyester comprising the reactionproduct of an anhydride of a polybasic organic carboxylic acid and ahydroxyl group containing semi-crystalline polyester.

(C) 1 to 90 parts by weight of a glycidyl group containing polyphenoxyresin having an epoxy equivalent weight of 150 to 1500 g/equiv.

(D) 0 to 85 parts by weight of a glycidyl group containing (meth)acrylate copolymer having an epoxy equivalent weight of 1.0 to 5.0milli-equivalents of epoxy/gram of polymer.

(E) 0 to 20 parts by weight of a curing agent different from (C) and (D)and having functional groups reactable with the polyester (A) and (B)carboxylic acid groups.

Said thermosetting compositions are particularly suitable for lowtemperature cure powder applications on metal and heat sensitivesubstrates, which provide excellent coating appearance and mechanicalproperties.

The current invention solves the problems of low flow, poor appearanceand inferior mechanical properties encountered in conventional lowtemperature cure powder coatings.

The carboxyl functional amorphous polyester (A) used in the compositionaccording to the invention is preferably composed of, referring to thepolyacid constituents, from 50 to 100 molar percent of terephthalic orisophthalic acid or their mixtures and from 50 to 0 molar percent ofanother aliphatic, cycloaliphatic or aromatic polyacid, and, referringto the polyol constituents, from 40 to 100 molar percent of neopentylglycol and from 60 to 0 molar percent of another aliphatic and/orcycloaliphatic polyol. Branching of the amorphous polyester can beobtained by incorporation of a polyacid or polyol.

The carboxyl functional semi-crystalline polyester (B) used in thecomposition according to the invention is preferably obtained from thering-opening reaction of the anhydride group of a trimellitic and/orpyromellitic anhydride with a hydroxyl group containing semi-crystallinepolyester (b). This hydroxyl-group containing semi-crystalline polyester(b)which is preferably composed of, referring to the polyacidconstituents, from 70 to 100 molar percent of terephthalic acid,1,4-cyclohexanedicarboxylic acid or a linear chain dicarboxylic acidcontaining 4 to 16 carbon atoms and from 30 to 0 molar percent ofanother aliphatic, cycloaliphatic or aromatic polyacid, and, referringto the polyol constituents, from 70 to 100 molar percent of acycloaliphatic or a linear chain aliphatic polyol containing 2 to 16carbon atoms and from 30 to 0 molar percent of another aliphatic orcycloaliphatic polyol. This hydroxyl-group containing polyester (b)preferably has an hydroxylnumber of 15 to 70 mg KOH/g.

The glycidyl group containing polyphenoxy resin (C) used in thecomposition according to the invention is preferably from the BisphenolA or from the phenol or cresol novolac type.

The glycidyl group containing acrylic copolymer (D) optionally used inthe composition according to the invention is preferably prepared from10 to 90 molar percent of a glycidyl group containing monomer and from90 to 10 molar percent of one or more other monomers copolymerizablewith the glycidyl group containing monomer.

The curing agent having functional groups reactive with the carboxylicacid groups of the polyesters (E) optionally used in the compositionaccording to the invention is preferably a polyepoxy orβ-hydroxyalkylamide compound.

The carboxyl functional amorphous polyesters (A) of the presentinvention have an acid number from 15 to 100 mg KOH/g and preferablyfrom 30 to 70 mg KOH/g.

Preferably, the carboxyl functional amorphous polyesters have:

-   -   a number averaged molecular weight ranging from 1100 to 15000        and more preferably from 1600 to 8500, measured by gel        permeation chromatography (GPC)    -   a glass transition temperature Tg) from 40 to 80° C., measured        by Differential Scanning Calorimetry according to ASTM D3418        with a heating gradient of 20° C. per minute    -   an ICI cone and plate viscosity according to ASTM D4287-88,        measured at 200° C. ranging from 5 to 15000 mPa.s.

The acid constituent of the amorphous polyester, according to thepresent invention, is preferably from 50 to 100 molar percent composedof terephthalic or isophthalic acid or their mixtures and from 0 to 50molar percent of another polyacid constituent selected from one or morealiphatic, cycloaliphatic or aromatic polyacids, such as: fumaric acid,maleic acid, phthalic anhydride, 1,4-cyclohexanedicarboxylic acid,1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid,succinic acid, adipic acid, glutaric acid, pimelic acid, suberic acid,azealic acid, sebacic acid, 1,12-dodecanedioic acid, trimellitic acid orpyromellitic acid, etc., or the corresponding anhydrides.

The glycol constituent of the amorphous polyester, according to thepresent invention, is preferably from 40 to 100 molar percent composedof neopentyl glycol and from 0 to 60 molar percent of another glycolconstituent selected from one or more aliphatic or cycloaliphaticglycols such as: ethylene glycol, propylene glycol, 1,4-butanepolyol,1,6-hexanepolyol, 1,4-cyclohexanepolyol, 1,4-cyclohexanedimethanol,2-methyl-1,3-propanepolyol, 2-butyl-2-ethyl-1,3-propanepolyol,hydrogenated Bisphenol A, hydroxypivalate of neopentyl glycol,trimethylolpropane, ditrimethylolpropane, pentaerythritol, etc.

The carboxyl functional semi-crystalline polyesters (B) used in thepresent invention preferably have a carboxyl number from 30 to 120 mgKOH/g and more preferably from 50 to 100 mg KOH/g and most preferablefrom 70 to 100 mg KOH/g.

Preferably, the carboxyl functional semi-crystalline polyesters arefurther characterized by:

-   -   a number averaged molecular weight ranging from 1100 to 17000        and more preferably from 1400 to 11200    -   a fusion zone from 50 to 150° C., measured by Differential        Scanning Calorimetry (DSC) according to ASTM D3418 with a        heating gradient of 20° C. per minute    -   a glass transition temperature (Tg) of below 40° C., measured by        Differential Scanning Calorimetry (DSC) according to ASTM D3418        with a heating gradient of 20° C. per minute    -   a degree of crystallinity, measured by Differential Scanning        Calorimetry (DSC) according to ASTM D3415 of at least 5 J/g and        preferably at least 10 J/g    -   an ICI (cone/plate) viscosity according to ASTM D4287-88,        measured at 100° C. of at least 10 mPa.s.

The acid constituent of the semi-crystalline polyester, according to thepresent invention, is preferably from 70 to 100 molar percent composedof terephthalic acid, 1,4-cyclohexanedicarboxylic acid or a linear chaindicarboxylic acid containing from 4 to 16 carbon atoms such as succinicacid, adipic acid, glutaric acid, pimelic acid, suberic acid, azelaicacid, sebacic acid, 1,10-decanedioic acid, 1,11-undecanedioic acid,1,12-dodecanedioic acid, 1,13-triadecanedioic acid,1,14-tetradecanedioic acid, 1,15-pentadecanedioic acid,1,16-hexadecanedioic acid, etc. used in a mixture or alone, and from 30to 0 molar percent of another aliphatic, cycloaliphatic or aromaticpolyacid such as fumaric acid, maleic anhydride, phthalic anhydride,isophthalic acid, 1,3-cyclohexanedicarboxylic acid,1,2-cyclohexanedicarboxylic acid, ect.

The glycol constituent of the semi-crystalline polyester, according tothe present invention, is preferably from 70 to 100 molar percentcomposed of a cycloaliphatic or linear-chain aliphatic polyol containing2 to 16 carbon atoms such as 1,4-cyclohexanepolyol,1,4-cyclohexanedimethanol, hydrogenated Bisphenol A,2,2,4,4-tetramethyl-1,3-cyclobutanol or4,8-bis[hydroxymethyl]tricyclo[5.2.1.O]decane, ethylene glycol,1,3-propanepolyol, 1,4-butanepolyol, 1,5-pentanepolyol,1,6-hexanepolyol, 1,7-heptanepolyol, 1,8-octanepolyol, 1,9-nonanepolyol,1,10-decanepolyol, 14-tetradecanepolyol, 1,16-hexadecanepolyol, etc.,used in a mixture or alone, and from 30 to 0 molar percent of anotheraliphatic glycol such as propylene glycol, neopentyl glycol,2-methyl-1,3-propanepolyol, 2-butyl-2-ethyl-1,3-propanepolyol,hydroxypivalate of neopentyl glycol, etc.

The glycidyl group containing polyphenoxy resin (C) used in thecomposition of the present invention is preferably selected from theBisphenol A based epoxy resins, phenol or cresol epoxy novolacs.

Bisphenol A based epoxy resins are typically prepared from the reactionof Bisphenol A and epichlorohydrin, wherein the excess ofepichlorohydrin determines the number average molecular weight of theepoxy resin. See W. G. Potter: Epoxide Resins, Springer-Verlag, New York(1970) and Y. Tanaka, A. Okada, I. Tomizuka in C. A. May, Y. Tanaka(eds.): Epoxy Resins Chemistry and Technology, Chapter 2, pp.9-134,Marcel Dekker, New York 1973.

The phenol and cresol epoxy novolacs are generally prepared by theacid-catalyzed condensation of formaldehyde with either phenol orcresol.

Epoxidation of the novolacs with epichlorohydrin furnishes the epoxynovolacs. Commercially available epoxy resins such as Epikote 1055 fromShell, Araldite GT7004 or Araldite ECN9699 from Ciba, D.E.R.664 from Dowand EPON 2002 from Shell are typical examples of glycidyl groupcontaining polyphenoxies.

The glycidyl group containing acrylic copolymers (D) optionally used inthe composition of the present invention have an epoxy equivalent weightof 1.0 to 5.0 milli-equivalents of epoxy/gram of polymer.

Preferably, the glycidyl group containing acrylic copolymers are furthercharacterized by:

-   -   a number averaged molecular weight ranging from 1000 to 15000    -   a glass transition temperature (T_(g)) from 40 to 85° C.        measured by Differential Scanning Calorimetry (DSC), according        to ASTM D3418 with a heating gradient of 20° C. per minute    -   an ICI cone and plate viscosity at 200° C. of at least 100 mPa.s

The glycidyl group containing monomer used to make the acrylic copolymerof the present invention is preferably used in molar percentages rangingfrom 10 to 90 and is preferably selected from the group of glycidylacrylate, glycidyl methacrylate, methyl glycidyl methacrylate, methylglycidyl acrylate, 3,4-epoxycyclohexylmethyl(meth)acrylate and acrylicglycidyl ether. They can be used alone or in mixtures of two or more.

Other monomers copolymerizable with the epoxy group containing monomerare preferably used In molar percentages ranging from 10 to 90 andselected from:

-   -   40 to 100 mole percentage of acrylic or methacrylic ester        monomers such as methyl acrylate, ethyl acrylate, n-propyl        acrylate, isopropyl acrylate, n-butyl acrylate, n-decyl        acrylate, methyl methacrylate, ethyl methacrylate, n-propyl        methacrylate, isopropyl methacrylate, n-butyl methacrylate,        isobutyl methacrylate, n-amyl methacrylate, n-hexyl        methacrylate, isoamyl methacrylate, allyl methacrylate,        sec-butyl methacrylate, tert-butyl methacrylate, 2-ethylbutyl        methacrylate, cinnamyl methacrylate, crotyl methacrylate,        cyclohexyl methacrylate, cyclopentyl methacrylate, methallyl        methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate,        2-phenylethyl methacrylate and phenyl methacrylate.    -   0 to 60 mole percent of other ethylenically unsaturated        copolymerizable monomers such as styrene, alkyl-substituted        styrenes and chloro-substituted styrenes, acrylonitrile, vinyl        chloride and vinylidene fluoride and vinyl acetate.

The curing agent (E) optionally used in the composition in accordance tothe present invention, having functional groups reactive with thepolyester's carboxylic acid groups, is preferably selected from:

-   -   polyepoxy compounds, which are solid at room temperature and        contain at least two epoxy groups per molecule, such as, for        example, triglycidyl isocyanurate (TGIC) diglycidyl        terephthalate, triglycidyl trimellitate, or mixutres thereof,        and Araldite FP910 or PT 912 both manufactured by Ciba.    -   β-hydroxyalkylamides which contains at least one, preferably two        bis(β-hydroxyalkyl)amide groups such as those mentioned in U.S.        Pat. Nos. 4,727,111, 4,788,255, 4,076,917, EP 322,834 and EP        473,380.

The carboxylic acid group containing amorphous polyester (A) and thehydroxyl group containing semi-crystalline polyester (b), according tothe present invention, may be prepared using conventional esterificationtechniques well known in the art. The polyesters are preferably preparedaccording to a procedure consisting of one or more reaction steps.

For the preparation of these polyesters, a conventional reactor equippedwith a stirrer, an inert gas (nitrogen) inlet, a thermocouple, adistillation column connected to a water-cooled condenser, a waterseparator and a vacuum connection tube are used.

The esterification conditions used to prepare the polyesters areconventional, namely a standard esterification catalyst, such asdibutyltin oxide, dibutyltin dilaurate, n-butyltin trioctoate, sulfuricacid or a sulphonic acid, can be used in an amount from 0.05 to 1.50% byweight of the reactants and optionally, color stabilizers, for example,phenolic antioxidants such as Irganox 1010 (Ciba) or phosphonite- andphosphite-type stabilizers such as tributylphosphite, can be added in anamount from 0 to 1% by weight of the reactants.

Polyesterification is generally carried out at a temperature which isgradually increased from 130° C. to about 190 to 250° C., first undernormal pressure, then, when necessary, under reduced pressure at the endof each process step, while maintaining these operating conditions untila polyester with the desired hydroxyl and/or acid number is obtained.The degree of esterification is monitored by determining the amount ofwater formed in the course of the reaction and the properties of theobtained polyester, for example, hydroxyl number, acid number, andviscosity.

The carboxylic acid group containing semi-crystalline polyester (B) isgenerally obtained by the ring opening reaction of the anhydride groupof a carboxylic acid anhydride with the hydroxyl group of the hydroxylgroup containing semi-crystalline polyester (b) at a temperature of from120 to 200° C.

To the carboxylic acid group containing amorphous and semi-crystallinepolyesters, crosslinking catalysts can optionally be added. Thesecatalysts are added in order to accelerate crosslinking reactions of thethermosetting powder composition during curing. Examples of suchcatalysts include amines (e.g. 2-phenylimidazoline), phosphines (e.g.triphenylphosphine), ammonium salts (e.g. tetrabutylammonium bromide ortetrapropylammonium chloride), phosphonium salts (e.g.ethyltriphenylphosphonium bromide (BETP) or tetrapropylphosphoniumchloride). These catalysts are preferably used in an amount of from 0.1to 5% with respect to the weight of the binder.

The carboxylic acid group containing semi-crystalline polyesters used inthe composition according to the present invention is more preferably acarboxylic acid anhydride end-capped semi-crystalline polyester,prepared from the ring-opening reaction of the anhydride group of atleast one, and preferably two mole(s), of a carboxylic acid anhydride,e.g. trimellitic anhydride, with one mole of hydroxyl functionalprepolymers having hydroxyl numbers of from 15 to 70 mg KOH/g, which wasprepared from the polycondensation of:

-   -   1,4-cyclohexanedicarboxylic acid and a linear chain aliphatic        C2-C16 polyol, or    -   a linear chain aliphatic C4-C16 polyacid and a linear chain        aliphatic C2-C16 polyol or a cycloaliphatic polyol

Particularly preferred carboxylic acid anhydride end-cappedsemi-crystalline polyesters are those prepared from the ring openingreaction of two moles of anhydride, especially trimellitic anhydride,with one mole of hydroxyl functional prepolymers prepared from thecondensation of:

-   -   1,4-cyclohexandicarboxylic acid and ethylene glycol,        1,4-butanepolyol or 1,6-hexanepolyol, or    -   1,12-dodecanedioic acid and ethylene glycol, 1,4-butanepolyol,        1,6-hexanepolyol or 1,4-cyclohexanedimethanol, or    -   1,4-cyclohexanedimethanol and succinic acid, adipic acid or        azelaic acid.

These trimellitic anhydride end-capped semi-crystalline polyesters havea sharp melting zone, a high degree of crystallinity, a high reactivitytowards reactable groups of crosslinkers, and properties that aredifferent from those found in the semi-crystalline polyesters known fromanterior arts.

Used in the thermosetting powder coating compositions of the presentinvention, they provide high reactivity, excellent flow and good storagestability,

The glycidyl group containing acrylic copolymer (D) can be prepared byconventional polymerization techniques, either in mass, in emulsion, orin the solution of an organic solvent. The nature of the solvent used isvery little of importance, provided that it is inert and that it readilydissolves the monomers and the synthesized copolymer. Suitable solventsinclude toluene, ethyl acetate, butyl acetate, xylene, etc. The monomersare generally copolymerized in the presence of a free radicalpolymerization initiator (benzoyl peroxide, dibutyl peroxide,azo-bis-isobutyronitrile, and the like) in an amount representing 0. 1to 4.0% by weight of the monomers.

To achieve a good control of the molecular weight and its distribution,a chain transfer agent, preferably of the mercaptan type, such asn-dodecylmercaptan, t-dodecanethiol, iso-octylmercaptan, or of thecarbon halide type, such as carbon tetrabromide, bromotrichloromethane,etc., can also added in the course of the reaction. The chain transferagent is usually used in amounts of up to 10% by weight of the monomersused in the copolymerization.

A cylindrical, double walled reactor equipped with a stirrer, acondenser, an inert gas (nitrogen, for example) inlet and outlet, andmetering pump feeding systems is generally used to prepare the glycidylgroup containing acrylic copolymer. Polymerization is carried out underconventional conditions. Thus, when polymerization is carried out insolution, for example, an organic solvent is first introduced into thereactor and heated to the refluxing temperature under an inert gasatmosphere (nitrogen, carbon dioxide, and the like) and a homogeneousmixture of the required monomers, the free radical polymerizationinitiator and the chain transfer agent, when needed, is then added tothe solvent gradually over several hours. The reaction mixture is thenmaintained at the indicated temperature for certain hours, whilestirring. The solvent Is then removed from the copolymer obtained invacuo.

The binder system of the thermosetting composition of the invention isgenerally composed in such a way that for each equivalent of carboxylgroup present in the amorphous polyester (A) and semi-crystallinepolyester (B), there is between 0.3 and 2.0 and preferably between 0.6and 1.7 equivalents of epoxy groups from the polyphenoxy resin (C),optionally the acrylic copolymer (D) and the curing agent (E). Theparticular thermosetting polyester blend (A) and (B), can be obtained bydry blending the amorphous and the semi-crystalline polyester using amechanical mixing procedure as available for the premixing of the powderpaint constituents.

Alternatively, the amorphous and the semi-crystalline polyester can beblended in the melt using the conventional cylindrical double-walledreactor or by extrusion such as the Betol BTS40.

In addition to the essential components described above, compositionswithin the scope of the present invention can also include flow controlagents such as Resiflow P-67 (Estron), Modaflow (Monsanto), Acronal 4F(BASF), etc., and degassing agents such as Benzoin (BASF) etc. To theformulation UV-light absorbers such as Tinuvin 900 (Ciba), hinderedamine light stabilizers represented by Tinuvin 144 (Ciba), otherstabilizing agents such as Tinuvin 312 and 1130 (Ciba), antioxidantssuch as Irganox 1010 (Ciba) and stabilizers of phosphonite or phosphitetypes, can also be added.

Both pigmented and clear lacquers can be prepared. A variety of dyes andpigments can be utilized in the composition of this invention. Examplesof useful pigments and dyes are: metallic oxides such as titaniumdioxide, iron oxide, zinc oxide and the like, metal hydroxides, metalpowders, sulphides, sulphates, carbonates, silicates such as ammoniumsilicate, carbon black, talc, china clay, barytes, iron blues, leadblues, organic reds, organic maroons and the like.

The components of the composition according to the invention may bemixed by dry blending in a mixer or blender (e.g. drum mixer). Thepremix is then homogenized at temperatures ranging from 50 to 120° C. ina single screw extruder such as the BUSS-Ko-Kneeter or a twin screwextruder such as the PRISM or APV. The extrudate, when cooled down, isground to a powder with a particle size ranging from 10 to 150 μm. Thepowdered composition may be deposited on the substrate by use of apowder gun such as an electrostatic CORONA gun or TRIBO gun. On theother hand, well known methods of powder deposition such as thefluidized bed technique can also be used. After deposition the powder isheated to a temperature between 80 and 150° C., causing the particles toflow and fuse together to form a smooth, uniform, continuous,non-cratered coating on the substrate surface.

The following examples are submitted for a better understanding of theinvention without being restricted thereto.

EXAMPLE A

A trimellitic anhydride end-capped crystalline polyester was preparedbased on the following mixture of ingredients: Ingredients Parts byweight (g) Dodecanedioic acid 4127.2 1,4-butanepolyol 1784.2 Trimelliticanhydride 721.3 Fascat 4102¹ 13.2¹Fascat 4102 is butyltin tris(2-ethylhexanoate) available from Atofina.

The dodecanedioic acid, 1,4-butanepolyol and Fascat 4102 were charged toa reaction vessel and heated under a nitrogen atmosphere until all theingredients melted. The temperature of the reaction mixture wasgradually increased to 220° C. The mixture was stirred and held at 220°C. until an acid value of below 5 mg KOH/g was obtained. The reactionmixture was then cooled to 170-190° C. followed by the addition of thetrimellitic anhydride. The temperature was maintained until the reactionmixture became clear and an acid value of 70-80 mg KOH/g was obtained.Vacuum was applied to remove water to push the polycondensation tocompletion. The reaction mixture was transferred from the vessel to areceiving container and allowed to cool to room temperature to give asolid product. The resultant polyester had an acid number of 78 mgKOH/g, a melt viscosity at 100° C. measured by Brookfield Cone and PlateViscometer of 5.5 poise, a melting temperature measured by DifferentialScanning Colorimeter (DSC) of 58.9° C.

EXAMPLE B

A trimellitic anhydride end-capped crystalline polyester was preparedbased on the following mixture of ingredients: Ingredients Parts byweight (g) Dodecanedioic acid 3692.0 1,6-hexanepolyol 2143.8 Trimellticanhydride 729.3 Fascat 4102 12.6

The dodecanedioic acid, 1,6-hexanepolyol and Fascat 4102 were charged toa reaction vessel and heated under a nitrogen atmosphere until all theingredients melted. The temperature of the reaction mixture wasgradually increased to 230° C. The mixture was stirred and held at 230°C. until an acid value of below 5 mg KOH/g was obtained. The reactionmixture was then cooled to 170-190° C. followed by the addition of thetrimellitic anhydride. The temperature was maintained until the reactionmixture became clear and an acid value of 70-80 mg KOH/g was obtained.Vacuum was applied to remove water to push the polycondensation tocompletion. The reaction mixture was transferred from the vessel to areceiving container and allowed to cool to room temperature to give asolid product. The resultant polyester had an acid number of 76 mgKOH/g, a melt viscosity at 100° C. measured by Brookfield Cone and PlateViscometer of 6.5 poise, a melting temperature measured by DifferentialScanning Colorimeter (DSC) of 60.0° C.

EXAMPLE C

A carboxylic acid group containing amorphous polyester was preparedbased on the following mixture of ingredients: Ingredients Parts byweight (g) Terephthalic acid 5389.1 Adipic acid 598.8 Neopentyl glycol4130.2 Trimelltic anhydride 1198.8 Fascat 4102 25.0

The terephthalic acid and adipic acid were charged to a reaction vesselcontaining molten neopentyl glycol and Fascat 4102 at a temperature of150° C. and under a nitrogen atmosphere. The temperature of the reactionmixture was gradually increased to 230° C. The mixture was stirred andheld at 230° C. until an acid value of below 5 mg KOH/g was obtained.Vacuum was applied to remove water to push the polycondensation tocompletion. The reaction mixture was then cooled to 170-190° C. followedby the addition of the trimellitic anhydride. The temperature wasmaintained until the reaction mixture became clear and an acid value of70-82 mg KOH/g was obtained. The reaction mixture was transferred fromthe vessel to a receiving container and allowed to cool to roomtemperature to give a solid product. The resultant polyester had an acidnumber of 80 mg KOH/g, a melt viscosity at 175° C. measured byBrookfield Cone and Plate Viscometer of 90 poise, a glass transitiontemperature measured by Differential Scanning Colorimeter (DSC) of 63.3°C.

EXAMPLE D

A glycidyl group containing acrylic copolymer was prepared based on thefollowing procedure:

800 parts of n-butyl acetate are charged in a 5-litre, double walledflask equipped with a stirrer, a water-cooled condenser, an inlet fornitrogen and a thermocouple attached to a thermo-regulator. The flaskcontent is then heated and stirred continuously while nitrogen is purgedthrough the solvent. At 125° C. a mixture of 91 parts oftert-butylperoxybenzoate in 200 parts of n-butyl acetate are fed in theflask during 215 minutes with a peristaltic pump. 5 Minutes after thefeeding, the other pump is started to feed the mixture of 284 parts ofglycidyl methacrylate, 312 parts of butyl methacrylate and 312 parts ofmethyl methacrylate within 180 minutes. The total synthesis time was 315minutes.

After evaporation of the n-butyl acetate an acrylic copolymer withfollowing characteristics was obtained: ICI viscosity @ 200° C.  400poise M_(n) 2600

EXAMPLE E

A pigmented low temperature cure powder coating composition was preparedbased on the following mixture of ingredients: Ingredients Parts byweight (g) Example C 136 Crystalline Polyester prepared in Example A 34EPON 2002 170 TiO₂ 150 Resiflow P-67 5 Benzoin 2 BETP 1.5

The ingredients were pre-mixed, melt blended at 90° C. in a Prism TSE 16PC Twin Screw Extruder. The extrudate was chilled and broken intoflakes, which were particulated, classified and electrostaticallysprayed onto metal or MDF panels and cured at 130° C. for 20 minutes.The properties of the resultant coating are reported in Table 1 below.

EXAMPLE F

A pigmented low temperature cure powder coating composition was preparedbased on the following mixture of ingredients: Ingredients Parts byweight (g) Example C 127.5 Crystalline Polyester prepared in Example B42.5 EPON 2002 170 TiO-2 149.5 Resiflow P-67 5 Benzoin 3.5 BETP 2

The ingredients were pre-mixed, melt blended at 85° C. in a Prism TSE 16PC Twin Screw Extruder. The extrudate was chilled and broken intoflakes, which were particulated, classified and electrostaticallysprayed onto metal or MDF panels and cured at 130° C. for 20 minutes.The properties of the resultant coating are reported in Table 1 below.

EXAMPLE G

A pigmented low temperature cure powder coating composition was preparedbased on the following mixture of ingredients: Ingredients Parts byweight (g) Example C 127.5 Crystalline Polyester prepared in Example B42.5 EPON 2002 150 Glycidyl acrylic copolymer of Example D 20 TiO₂ 149.5Resiflow P-67 5 Benzoin 3.5 BETP 2.0

The ingredients were pre-mixed, melt blended at 90° C. in a Prism TSE 16PC Twin Screw Extruder. The extrudate was chilled and broken intoflakes, which were particulated, classified and electrostaticallysprayed onto metal or MDF panels and cured at 130° C. for 25 minutes.The properties of the resultant coating are reported in Table 1 below.TABLE 1 Reverse MEK Example Gloss Impact Double Visual No. 60° 20° DOI(in. lb.) Rubs Appearance E 99.5 94.2 80 160 >100 smooth F 99.0 95.0 80160 >100 smooth G 100.0 94.2 80 80 >100 fairly smooth

1. A thermosetting coating composition comprising a binder wherein 100parts by weight of this binder comprises: (A) 1 to 50 parts by weight ofa carboxylic acid group containing amorphous polyester having an acidnumber of from 15 to 100 mg KOH/g. (B) 1 to 50 parts by weight of acarboxylic acid group containing semi-crystalline polyester, saidpolyester comprising the reaction product of an anhydride of a polybasicorganic carboxylic acid and a hydroxyl group containing semi-crystallinepolyester. (C) 1 to 90 parts by weight of a glycidyl group containingpolyphenoxy resin having an epoxy equivalent weight of 150 to 1500g/equiv. (D) 0 to 85 parts by weight of a glycidyl group containing(meth) acrylate copolymer having an epoxy equivalent weight of 1.0 to5.0 milli-equivalents of epoxy/gram of polymer. (E) 0 to 20 parts byweight of a curing agent different from (C) and (D) and havingfunctional groups reactable with the polyester (A) and (B) carboxylicacid groups.
 2. The composition according to claim 1 wherein thecarboxylic acid group containing amorphous polyester (A) is composed offrom 50 to 100% mole of terephthalic acid or isophthalic acid or theirmixtures and from 0 to 50% mole of an aliphatic, cycloaliphatic oraromatic polyacid different from terephthalic acid or isophthalic acid,referring to the polyacid constituents, and from 40 to 100% mole ofneopentyl glycol and from 0 to 60% mole of another aliphatic and/orcycloaliphatic polyol referring to the polyol constituents.
 3. Thecomposition according to claim 1 wherein the carboxylic acid groupcontaining semi-crystalline polyester (B) is obtained from the ringopening reaction of the anhydride group of trimellitic anhydride and/orpyromellitic anhydride with a hydroxyl group containing semi-crystallinepolyester having a hydroxyl number of from 15 to 70 mg KOH/g, andcomprising from 70 to 100% mole of terephthalic acid, 1,4-cyclohexanedicarboxylic acid or a linear chain dicarboxylic acidcontaining 4 to 16 carbon atoms and from 0 to 30% mole of anotheraromatic, aliphatic or cycloaliphatic polyacid, referring to thepolyacid constituents, and from 70 to 100% mole of a cycloaliphatic orlinear chain aliphatic polyol containing 2 to 16 carbon atoms and from 0to 30% mole of another aliphatic or cycloaliphatic polyol, referring tothe polyol constituents.
 4. The composition according to claim 1 whereinthe glycidyl group containing polyphenoxy resin (C) is a Bisphenol Abased epoxy resin or a phenol or cresol epoxy Novolac.
 5. Thecomposition according to claim 1 wherein the glycidyl group containing(meth)acrylate copolymer (D) is prepared from 10 to 90% mole of aglycidyl group containing monomer and from 90 to 10% mole of one or moremonomer copolymerizable with the glycidyl group containing monomers,said (meth)acrylate copolymer having a number averaged molecular weightof from 1000 to
 15000. 6. The composition according to claim 1 whereinthe curing agent (E) is triglycidyl isocyanurate, diglycidylterephthalate, triglycidyl trimellitate, or a mixture of them, or aβ-hydroxyalkylamide group containing compound.
 7. The compositionaccording to claim 1 wherein the carboxylic acid group containingamorphous polyester (A) has the following properties: a number averagedmolecular weight of from 1 100 to 15000, a glass transition temperature(Tg) from 40 to 80° C. and an ICI (cone/plate) viscosity at 200° C.ranging from 5 to 15000 mPa.s.
 8. The composition according to claim 7wherein the carboxylic acid group containing amorphous polyester (A) hasan acid number of from 30 to 70 mg KOH/g.
 9. The composition accordingto claim 1 wherein the carboxylic acid group containing semi-crystallinepolyester (B) has the following properties: an acid number from 30 to120 mg KOH/g, a number average molecular weight ranging from 1 100 to17000, a fusion zone from 50 to 150° C., a glass transition temperature(Tg) below 40° C., a degree of crystallinity of at least 5 J/g, and anICI (cone/plate) viscosity at 100° C. of at least 10 mPa.s.
 10. Thecomposition according to claim 9 wherein the acid number of (B) is from50 to 100 mg KOH/g.
 11. The composition according to claim 1 wherein theglycidyl group containing acrylic copolymer (D) has the followingproperties: a number average molecular weight ranging from 1000 to15000, a glass transition temperature (Tg) from 40 to 85° C., measuredby Differential Scanning Calorimetry (DSC), according to ASTM D3418 witha heating gradient of 20° C. per minute, and an ICI (cone/plate)viscosity determined by the ICI method at 200° C. of at least 100 mPa.s.12. The composition according to claim 1 containing from 0.1 to 5.0parts by weight, referring to 100 parts of binder, of a catalyzingcompound selected from the group consisting of amine, phosphine,ammonium salt and phosphonium salt catalysts.
 13. The compositionaccording to claim 1 additionally containing: UV-light absorbers and/orhindered amine light stabilizers, flow control agents, and/or degassingagents.
 14. A clear lacquer containing the thermosetting powdercomposition of claim
 1. 15. The thermosetting powder coating compositionaccording to claim 1 additionally containing at least one of pigments,dyes and fillers.
 16. A method for applying the thermosetting powdercomposition of claim 1 which comprises applying it by an electrostaticor friction charging spray gun or fluidized bed technique.
 17. Anentirely or partially coated substrate, wherein the coating materialused, is a powder coating composition containing the compositionaccording to claim 1.